This invention relates generally to turbine engines and more particularly, to methods and apparatus for assembling gas turbine engines.
At least some known gas turbine engines include combustors which ignite fuel-air mixtures which are then channeled through a turbine nozzle assembly towards a turbine. Some known turbine nozzle assemblies include a plurality of arcuate nozzle segments arranged circumferentially. At least some known turbine nozzles include a plurality of circumferentially-spaced hollow airfoil vanes coupled by integrally-formed inner and outer band platforms. More specifically, the inner band forms a portion of the radially inner flowpath boundary and the outer band forms a portion of the radially outer flowpath boundary.
To facilitate improving engine efficiency, at least some known engine assemblies include a seal, commonly known as a leaf seal, coupled between the turbine nozzle outer band and an aft end of the combustor. Known leaf seals are retained in position via a plurality of coil springs coupled to a plurality of fasteners that extend through radial tabs extending from the outer band. The coil springs enable the leaf springs to shift during engine operations. Because of the orientation of known turbine nozzle radial tabs, one end of known leaf springs is unsupported. In such engine assemblies, when combustion gases discharged from the combustor approach the nozzle vane leading edge, a pressure or bow wave may be formed from the vane leading edge stagnation and propagate a distance upstream from the nozzle assembly. Such bow waves may induce circumferential pressure variations across the leaf seal. Over time, exposing the leaf seal to such pressure variations may cause cracks to develop along the seal. Specifically, the unsupported free end of the leaf seal may break thus decreasing engine efficiency and/or, depending on the extent of the damage, may render the engine inoperable.
FIG. 1 is a side view of an exemplary known turbine nozzle 50 that may be used with a gas turbine engine. FIG. 2 is a perspective view of turbine nozzle 50. In the exemplary embodiment, nozzle 50 is one segment of a plurality of segments that are positioned circumferentially to form a nozzle assembly (not shown) within the gas turbine engine. Nozzle 50 includes at least one airfoil vane 52 that extends between an arcuate radially outer band or platform 54, and an arcuate radially inner band or platform 56. More specifically, in the exemplary embodiment, outer band 54 and the inner band 56 are each integrally-formed with airfoil vane 52.
Vane 52 includes a pressure-side sidewall 60 and a suction-side sidewall 62 that are connected at a leading edge 64 and at a chordwise-spaced trailing edge 66 such that a cooling cavity 68 is defined between sidewalls 60 and 62. Vane sidewalls 60 and 62 each extend radially between bands 54 and 56 and in the exemplary embodiment, sidewall 60 is generally concave, and sidewall 62 is generally convex.
Outer and inner bands 54 and 56 each include a leading edge 70 and 72, respectively, a trailing edge 74 and 76, respectively, and a platform body 78 and 80, respectively, extending therebetween. In the exemplary embodiment, airfoil vane(s) 52 are oriented such that outer and inner band leading edges 70 and 72, respectively, are each a distance d upstream from airfoil vane leading edge 64. Distance d is variably selected to ensure that leading edges 70 and 72 are upstream from vane leading edge 64, and to facilitate preventing hot gas injections along vane leading edge 64, as described in more detail below.
In the exemplary embodiment, inner band 56 includes an aft flange 90 that extends radially inwardly therefrom. More specifically, flange 90 extends radially inwardly from band 56 with respect to a radially inner surface 92 of band 56. Inner band 56 also includes a forward flange 94 that extends radially inward therefrom. Forward flange 94 is positioned between inner band leading edge 72 and aft flange 90, and extends radially inwardly from band 56. In the exemplary embodiment, an upstream side 100 of forward flange 94 is substantially planar between a radially outermost surface 102 of flange 94 and radially inner surface 92. Moreover, in the exemplary embodiment, a downstream side 106 of flange 94 is substantially planar from flange surface 102 to radially inner surface 92.
Inner band 56 also includes a plurality of circumferentially-spaced radial tabs 110 that extend radially inwardly therefrom. More specifically, in the exemplary embodiment, the number of radial tabs 110 extending from inner band 56 is the same as the number of vanes 52. In the exemplary embodiment, each tab 110 includes substantially parallel upstream and downstream surfaces 120 and 122, respectively. Radial tabs 110 are spaced a distance d2 downstream from forward flange 94 such that a retention channel 130 is defined between each radial tab 110 and forward flange 94.
In the exemplary embodiment, outer band 54 includes an aft flange 140 that extends generally radially outwardly therefrom. More specifically, flange 140 extends radially outwardly from band 54 with respect to a radially outer surface 142 of band 54. Outer band 54 also includes a forward flange 144 that extends radially outward therefrom. Forward flange 144 is positioned between outer band leading edge 70 and aft flange 140, and extends radially outward from band 54. In the exemplary embodiment, an upstream side 146 of forward flange 144 is substantially planar between a radially outermost surface 147 of flange 144 and band radially outer surface 142. Moreover, in the exemplary embodiment, a downstream side 148 of flange 144 is substantially planar from flange surface 147 to radially outer surface 142.
Outer band 54 also includes a plurality of circumferentially-spaced radial tabs 160 that extend radially outwardly therefrom. More specifically, in the exemplary embodiment, the number of radial tabs 160 is the same as the number of vanes 52. In the exemplary embodiment, each tab 160 includes substantially parallel upstream and downstream surfaces 162 and 164, respectively. Radial tabs 160 are spaced a distance d3 downstream from forward flange 144 such that a retention channel 166 is defined between each radial tab 160 and forward flange 144.
In the exemplary embodiment, channels 166 are approximately the same size as channels 130.
In the exemplary embodiment, inner band 56 includes a circumferentially-adjacent leaf seal assembly 168 including a seal 170 that is positioned between forward flange 94 and radial tab 110. Moreover, in the exemplary embodiment, each nozzle assembly 50 includes one seal 170. In an alternative embodiment, each nozzle assembly 50 includes more than one seal 170. In another alternative embodiment, one seal 170 extends across two or more circumferentially-adjacent nozzle assemblies 50. Seal 170 is positioned adjacent forward flange 94 and is coupled to radial tab 110 via a fastener 172, such as a coil spring, as illustrated in the exemplary embodiment, that extends through an aperture 174 defined in radial tab 110. As will be appreciated by one skilled in the art, seal 170 may be coupled to radial tab 110 with any suitable coupling mechanism that functions as described herein. In the exemplary embodiment, a spring 176 circumscribes fastener 172 and is positioned between forward flange 94 and radial tab 110.
In the exemplary embodiment, outer band 54 includes a circumferentially-adjacent leaf seal assembly 178 including a seal 180 that is positioned between forward flange 144 and radial tab 160. More specifically, in the exemplary embodiment, each nozzle assembly 50 includes one seal 180. In an alternative embodiment, each nozzle assembly 50 includes more than one of seal 180. In another alternative embodiment, one seal 180 extends across two or more circumferentially-adjacent nozzle assemblies 50. Seal 180 is positioned adjacent forward flange 144 and is coupled to radial tab 160 via a fastener 182, such as a coil spring, as illustrated in the exemplary embodiment, that extends through an aperture 184 defined in radial tab 160. As will be appreciated by one skilled in the art, seal 180 may be coupled to radial tab 160 with any suitable coupling mechanism that functions as described herein. In the exemplary embodiment, a spring 186 circumscribes fastener 182 and is positioned between forward flange 144 and radial tab 160.